This is a clinical research study of a new investigational anti-HIV medication, GW433908. GW433908 is a new form of amprenavir, a protease inhibitor, used to treat HIV infection. The current form of amprenavir requires patients to take a large number of capsules. GW433908 gets into the body more easily and reduces the number of pills patients have to take. The purpose of this study is to find the best dose of GW433908. This will be done by determining which dose of GW433908 gives similar blood concentrations to the marketed dose of amprenavir capsules. Eligible study subjects receive an experimental combination of abacavir, lamivudine and GW433908/amprenavir. Abacavir and lamivudine are from the nucleoside reverse transcriptase inhibitor (NRTI) class and amprenavir and GW433908 are from the protease inhibitor class of anti-HIV drugs. Both classes block enzymes that are necessary for the HIV virus to make copies of itself. With the exception of G@433908, the medications used in this study have been shown to decrease the amount of HIV virus in the blood and increase the CD4+ lymphocyte counts (white blood cells that fight off specific infections).